The present invention is directed to a gas powered motor for rotating a bit for operation in a well for various functions.
For example, scale usually accumulates during steam production in geothermal well bore production strings. This scale buildup restricts flow and will eventually cause the well to stop producing. Therefore, the scale on the inside of the well production string must be periodically removed.
Various equipment has been tried for removing scale. High temperatures in geothermal wells preclude the use of conventional mud motors. The dynamic elastomer seals in such motors is affected by the high temperatures causing failure. Also fluid operated mud pump motors pump mud into the well causing the hydrostatic pressure in the well to become greater than the down hole pressure and results in killing the well. Success with vibratory impact motors is limited because the scale is broken instead of sheared. Scale which is broken in large fragments cannot be circulated completely out of the well and the scale will tend to fall back on the apparatus and create problems. Drilling rigs are another option used in scale cleanouts. Although drilling rigs are successful, they are quite expensive in most cases.
While gas driven motors have been attempted in the past, they have failed and have not been successful. The present application is directed to a gas powered apparatus, which will rotate a mill at a proper rpm and torque and control and limit these parameters in the hostile environment prevalent in geothermal wells. The rotating mill permits the scale to be sheared instead of broken allowing scale fragments to be efficiently circulated out of the well bore, the temperature effects on the apparatus is greatly reduced by the elimination of dynamic elastomer seals, and the motor is gas operated, such as by air or nitrogen, to eliminate the chances of killing the well by the actuating fluid.